This invention relates to high-pressure mercury-vapor lamps and, mor particularly, to such a lamp which incorporates a special phosphor mixture as a coating on the interior surface of the outer envelope in order to improve both the color rendition and light output of the lamp.
High-pressure mercury-vapor lamps which have a light emission modified by the use of phosphor mixtures are well known and one embodiment of such a lamp is described in U.S. Pat. No. 4,065,688, dated Dec. 27, 1977 to W. A. Thornton, the present applicant. The phosphors utilized include red-emitting yttrium vanadate or yttrium phosphate vanadate activated by trivalent europium. Another embodiment of such a lamp is described in U.S. Pat. No. 3,602,758 dated Aug. 31, 1971 to Thornton et al.
Apatite-structured strontium chlorophosphate activated by a divalent europium is a well-known narrow-band, blue-emitting phosphor and is disclosed in U.S. Pat. No. 4,038,204, dated Jul. 26, 1977 to Wachtel. Other such blue-violet emitting phosphors activated by divalent europium are known and are described in U.S. Pat. No. 3,937,998, dated Feb. 10, 1976 to Verstegen et al.
Calcium orthotellurate activated by uranium is a known phosphor which has a narrow emission in the blue-green peaking at about 500 nm. This phosphor is described in detail in Journal of Electrochemical Society, Volume 120, pgs. 660-664 (1973).
A method for preparing red-emitting yttrium vanadate phosphor activated by trivalent europium is disclosed in U.S. Pat. No. 3,630,946 dated Dec. 28, 1971 to Ropp, et al. and such phosphor is now well known.
The internationally accepted method for standardizing and measuring the color rendering properties of light sources is set forth in the publication of the International Commission on Illumination, identified as publication C.I.E. No. 13, (E-1.3.2.) 1965.